Searching for Substellar Companions with Keck and Gemini Adaptive Optics

1. Searching for Substellar Companions with Keck and Gemini Adaptive Optics K. L. Luhman (CfA) Collaborator: Ray Jayawardhana (UCB)

2. Outline 1. Introduction 2. Observing Strategy 3. Observing Sequence 4. Data Reduction and Analysis 5. Sample Images 6. Detection Limits

3. Introduction • Objective: • Obtain useful constraints on the frequency of wide brown dwarf and planetary companions. • Instruments and Telescopes: • Near-infrared adaptive optics imaging on Gemini and Keck • Keck AO+KCAM • 256x256, 17.43 mas/pixel, 4.46”x4.46” • Gemini Hokupa’a AO+QUIRC • 1024x1024, 19.74 mas/pixel, 20.2”x20.2” • Target Selection: • Require natural guide stars <30” from target and R<14 for • Keck and R<14-18 for Gemini • Sample: • extrasolar planetary systems and young stars

4. Observing Strategy • Saturation and Dynamic Range: • Short exposures in which target is not saturated • -> photometric calibration, detection of close companions • Long exposures that are background-limited far from primary • -> detection of faint wide companions • Keck targets = H=2-7 • -> short exposures w/ N3, N2, N1, open, long exp+open • Gemini targets = H=8-11 • -> exposures of 1 and 75 sec • Example: H=5 • 2.5 sec + N2 = not saturated • 2.5 sec + N1 = saturated • 2.5 sec + open = saturated • 25 sec + open = saturated at r<30 pix (<0.5”)

5. Observing Strategy • Latent Images and Flat Fielding: • Keck: • twilight sky flats • no latent images • Gemini: • • probing separations of <4” -> use 2x2 5” dithers and use diagonal frame as flat field • • prefer to obtain all short exposures before long exposures to avoid latent images, but wasn’t possible because of need to minimize filter changes • Photometric Calibration: • • Calibrate photometry with short exposures of the target • • For Gemini queue observations, can check against default calibration

6. Observing Strategy • Frequency of observations of PSF stars: • Keck: • Typical time lapse is ~10-20 min. • Gemini: • In reasonable observing strategy and given official overheads, the minimum time between images of target and PSF is ~30 min. • Choice of PSF stars: • • Prefer a PSF star that has is similar to target in magnitude, color, and position on sky. • • For both Keck and Gemini, most of our targets are grouped into pairs that are close together on the sky and the stars in a pair are used as PSF stars for each other.

7. Observing Strategy • Astrometry: • • Accurate positions of candidate companions relative to primary stars are needed for proper motion measurements. • -> Without moving telescope, obtain short unsaturated exposure of primary followed by the long exposures. • • Presence of multiple companions in field of view is helpful. • Registration of individual exposures: • • Registration is easily performed if unsaturated objects are detected in individual frames, which is more likely the larger field of view of Gemini data. • • Registration is more difficult when the only detected sources is the highly saturated primary. • -> For Keck data, obtain first half of exposures at 1 position and second half at a second position offset by 5, 5 pixels; sufficient for bad pixel rejection while making registration easier.

8. Observing Strategy • Choice of filters: • Use JHK expect multiple candidate companions or companions that are cool enough to show methane absorption. • Keck: • -> Most efficient to use only H and follow up candidates with more band, proper motion data, or spectroscopy. • Gemini: • -> Because of high official overhead per target, the additional time to use 3 filters rather than 1 is small.

9. Observing Sequence • Keck: • 1) center target #1 in upper left quadrant • 2) 10 x longest exp/least opaque filter that doesn’t saturate • 3) repeat filters N2, N1, open • 4) repeat 1-3 at target #2 • 5) return to #1, open+shortest exposure, offset to dead quadrant, 3 long exposures/dither/3 long exposures • 6) repeat 4 at 2 more PA’s (+120, +240) • 7) repeat 5-6 at #2 • Gemini: • 1) 1 sec exposure in 2x2 dither • 2) 2x75 sec exposures in 2x2 dither • 3) repeat 1-2 at 2 more filters • 4) repeat 1-3 at next target

10. Reduction and Analysis • Basic image reduction: • Dark subtraction, flat fielding • Registration: • Use faint sources or outer PSF of saturated target (but tricky • because of rotating PSF) • Keck image properties: • • point-like artifacts within seeing disk • • elongated artifacts outside of seeing disk • • rotating PSF • • waffle • • ghosts • Gemini image properties: • smoother PSF, fewer point-like artifacts

11. Reduction and Analysis • Close companions (<0.5”): • • Deconvolution is not useful because of rotation of PSF with time and the frequent saturation of the primary. • • Close companions must be identified by visually comparing to PSF star. • Wide companions (>0.5”): • PSF star is unnecessary; companions are easily identified visually

12. Keck N1+7 x 2s linear scale 4.46”x4.46”

13. Keck N1+7 x 2s log scale 4.46”x4.46”

14. Keck 8 x 2s log scale 4.46”x4.46”

15. Keck 12 x 30s log scale 4.46”x4.46”

16. Keck 12 x 30s linear scale 4.46”x4.46”

17. Gemini 4 x 1s linear scale 4.46”x4.46”

18. Gemini 4 x 1s log scale 4.46”x4.46”

19. Gemini 8 x 75s log scale 4.46”x4.46”

20. Gemini 8 x 75s linear scale 4.46”x4.46”

21. Gemini 8 x 75s linear scale 20”x20”

22. Gemini 4 x 1s log scale 2.37”x2.37”

23. Keck 8 x 2s log scale 2.37”x2.37”

24. Keck  Eri: H=1.6 N3+10 x 1.1s linear scale 2.23”x2.23”

25. Keck  Eri: H=1.6 N2+10 x 1.1s linear scale 2.23”x2.23”

26. Keck  Eri: H=1.6 N1+10 x 1.1s linear scale 2.23”x2.23”

27. Keck  Eri: H=1.6 1 x 1.1s linear scale 2.23”x2.23”

28. Keck  Eri: H=1.6 66 x 5s linear scale 4.46”x4.46”

29. H=8 at 5 min